A MODEL OF THE LEAF EXTENSION RATE OF TALL FESCUE IN RESPONSE TO NITROGEN AND TEMPERATURE

The leaf extension rate (LER) of tall fescue (Festuca arundinacea Schreb.) was studied in the field under various nitrogen and temperature regimes. The LER wa3 closely related to temperature when N was not limiting plant growth. Two distinct relationships between the LER and the temperature were obtained, one for vegetative growth and one for the reproductive period. These relationships, described by a Gompertz function, were exponential at temperatures below 8 °C and linear at temperatures above 8 °C. They made possible the calculation of an optimal LER corresponding to non-limiting N conditions for plant growth.The strong influence of the temperature on the LER was still observed under N limiting conditions. The N status of the swards was described by the ratio between the actual N content (Nactual) and the optimal N content (Noptimal)- The Noptimalwas defined as the N content experienced at a non-limiting level of N nutrition but without N luxuryconsumption. The Noptimalexpressed as a function of dry matter yield, declined during growth. The effect of the Nstatus of the swards on the LER was analysed by calculating the ratio between the actual LER and the optimal LER, and relating it to the ratio between actualand Noptimal. It was shown that these two ratios were highly correlated. © 1992 Annals of Botany Company.